بررسي سنگ‌شناختي و جايگاه زمين‌ساختي سنگ‌هاي آذرين ترشيري محدوده ندوشن‌ (جنوب‌غرب صدوق، استان يزد)

Determination of approximate center of mineralization and precipitation conditions of copper-gold using minerallography and fluids inclusions in the Kalchouyeh occurrence

سنگ‌هاي آذرين ترشيري محدوده ندوشن در كمربند ماگمايي اروميه- دختر و 130 كيلومتري جنوب‌غرب شهرستان يزد رخنمون دارند. بر اساس مطالعات كاني‌شناختي و ژيوشيميايي اين سنگ‌‌‌ها شامل داسيت، آندزيت، اليوين‌بازالت و توف‌هاي بلورين و نفوذي‌هاي ميكروگرانوديوريتي هستند. بر اساس نمودار‌هاي تكتونو‌ماگمايي Y-Nb، Y-Zr و Zr/Al2O3-TiO2/Al2O3 اين نمونه‌ها موقعيت تكتونيكي قوس ماگمايي را نشان مي‌دهند. همچنين در نمودار تمايزي Ce/P2O5-Zr/TiO2 كه براي تفكيك قوس‌هاي ماگمايي حاشيه فعال قاره‌اي از قوس‌هاي ماگمايي پس از ‌برخورد به‌كار برده مي‌شود، اين سنگ‌ها در محدوده قوس‌هاي پس از برخورد (PAP) قرار مي‌گيرند. در نمودار عنكبوتي به‌هنجار شده با MORB، سنگ‌هاي محدوده مورد مطالعه از عناصر HFSE تهي‌شدگي نشان داده كه مشخصه ماگماتيسم قوس آتشفشاني است. غني‌شدگي از K، Rb و Th و بي‌هنجاري‌ منفي عناصر Ti، Ta، Nb و P در اين سنگ‌ها نشانگر شكل‌گيري آن‌ها در منطقه فرورانش است.

The Kalchouyeh area, southwest of Nain is located in the Uromieh-Dokhtar volcano-plutonic belt. From the lithologic point of view, this area is mainly comprised of pyroxene andesite lavas, trachy- andesites, tuffic sand stones and lithic tuffs. Mineralization (Cu=Ave. 7637.755, Au=Ave. 0.55 ppm)occurred mainly as disseminations and veinlets hosted by trachy andesite and pyroxene andesites. Fluid inclusion and minerallographic studies were carried out to determine the direction and the source of the ore - bearing fluids. The two major mineralized zones: A (larger vein) from the North-Northwest and B (smaller vein) from the East-Southeast of the area were sampled. The alteration studies have revealed that the main alteration assemblages are comprised of silicification and propylitic. The ore minerals are chalcopyrite, galena, pyrite, bornite, chalcocite, covellite, goethite, malachite, azurite and cuprite with quartz, calcite and barite as the main gangues. By means of these evidences, it seems that two major processes that carry ore elements are diffusion adjacent to fractures and mainly infiltration into fractures. Petrographic studies on fluid inclusions indicate that most of them are circular to subhedral and in some cases elongated in shape. The most studied inclusions are two phases (L+V) type having a relatively big vapor bubble. The direction of ore bearing fluids movement is determined according to homogenization temperature, salinity of fluid inclusions and types of mineralization, from east-southeast to north-northwest. It seems that approximate site of mineralization center is located adjacent to small vein B. On the base of aforementioned evidences, the principle deposition mechanism of ore minerals was mixing of two meteoric and magmatic fluids and the mineralization is Low-sulphide epithermal in type.